Method and apparatus for safely ascending a utility tower

ABSTRACT

A support tower is equipped with a plurality of step-bolts, each of which comprises (1) a threaded portion that is attached to a pre-existing hole in the tower and (2) a shaft portion that extends outward from the tower. The shaft portion of each of the step-bolts includes an undercut section that is sized to match (with minimal clearance) the throat of a corresponding carabiner, which is attached to a safety harness worn by the user. The remainder of the shaft portion of the step-bolt is larger in diameter than the throat of the carabiner so that the carabiner cannot slide out toward the free end of the step-bolt.

This application claims priority of U.S. Provisional Patent Application62/331,950 filed on May 4, 2016.

BACKGROUND OF THE INVENTION

This invention relates generally to the repair and maintenance ofutility towers, radio and cell phone towers, telephone poles, utilitypoles and the like and, in particular, to methods and apparatus for thesafe ascending and descending of such towers and poles by linemen,repairmen and others.

It is well-known in the art to attach a series of step-bolts to utilitytowers, utility pylons, radio towers, cell phone towers, telephonepoles, utility poles and the like (hereinafter collectively referred toas a “support tower” or simply “tower”) to provide a foot purchaseand/or hand grip for a lineman, repairman or other authorized individualto use to ascend the tower. A conventional step-bolt, however, istypically nothing more than a cylindrical bolt between ⅝″ and ¾″ indiameter, with an enlarged head approximately 2″ in diameter, similar tothe head of a carriage bolt, which acts as a stop to prevent thelineman's foot from slipping off the end of the step-bolt.

Historically, lineman and communications tower workers would ascend autility tower by free climbing without any safety strap or harness,since this is the fastest way to ascend and descend the tower. However,in the aftermath of an epidemic of cell phone tower deaths (13 deaths in2013 and 11 deaths in 2014), OSHA and the communications industry havebegun to focus on methods of improving the safety of communicationstower workers. Similar efforts to improve worker safety are underway inthe power transmission industry. One method that has been implemented toimprove worker safety is to provide the worker with a wearable safetyharness, which can be attached to the tower step-bolts using a lanyardwith a carabiner attached to the end. Unfortunately, most commoncarabiners are designed primarily to attach to a D-ring or overheadcable, rather than to a cantilevered step-bolt. Therefore, a typicalcarabiner that has a gap between the nose and gate sufficient toaccommodate a ¾″ bolt will also have a basket that is larger than the2-inch diameter head of a standard step-bolt. Finally, a standardstep-bolt, while adequate to support the weight of a 95th percentilemale when climbing, will yield and bend downward under the shock load ofa falling worker, especially if the carabiner has moved to the extremefree end of the step-bolt, where the moment arm for the shock load isgreatest. These two defects could result in a carabiner slipping off theend of the step-bolt with potentially disastrous consequences.

It is also cumbersome to use a conventional carabiner since the gatemust be manipulated by hand (typically by holding the carabiner with onehand and pulling and twisting the gate with the other hand) each timethe carabiner is moved. Accordingly, many linemen and communicationsworkers prefer a purpose-built carabiner and safety lanyard such as the“Step Safe Lanyard 2002” sold by Total Access (UK) Ltd, Eccleshall UK.The Step Safe lanyard has a gate and lock that can both be manipulatedwith a single hand. It also has a basket (throat) that is sized toclosely-match the diameter of a step-bolt (i.e. ⅝″ and ¾″ in diameter)and therefore should not slip off the end of the step-bolt, even if thestep-bolt yields and bends downward. The Safe Step lanyard does not,however, have any way of preventing the carabiner from moving to thefree end of the step-bolt where the bending moment arm is greatest.

What is needed therefore, is the combination of a purpose-builtcarabiner, and a step-bolt configured to prevent the carabiner fromsliding to the outer end of the step-bolt. Preventing the carabiner fromsliding outward results in reduced bending loads on the step-bolt duringa fall arrest, eliminating the possibility that the step-bolt will benddownward (or fail completely).

SUMMARY OF THE INVENTION

The present invention solves the foregoing problem by providing a towerequipped with a plurality of step-bolts, and a method of using thestep-bolts to safely ascend or descend a tower using a carabinerattached to a safety lanyard. According to an illustrative embodiment,each of the step-bolts comprises a threaded portion that attaches topre-existing holes in the tower and a shaft portion that extends outwardfrom the tower. The shaft portion of each of the step-bolts includes anundercut section that is sized to match (with minimal clearance) thethroat of the carabiner, while the remainder of the shaft portion islarger in diameter than the throat of the carabiner. In one embodiment,the undercut section is centered about the midpoint of the shaft portionof the step-bolt, which prevents the carabiner from sliding out towardthe end of the step-bolt when attached. In another embodiment, theundercut section is offset inward from the midpoint of the shaft portionto further reduce the bending moment arm of the carabiner on thestep-bolt during a fall arrest. According to an illustrative method, asupport tower is provided with the step-bolts as described above. Theuser ascends and descends the tower by attaching the carabiner to theundercut region of one step-bolt while stepping on another of thestep-bolts. In another embodiment, a tower is provided with bolts havingan undercut region as described above, but which are too short to stepon. These short step-bolts (referred to hereinafter as carabiner bolts)are used solely for the purpose of attaching the carabiner. Otherstep-bolts, including conventional step-bolts, are used to support theuser's weight in the normal course of ascending and descending the towerin conjunction with the carabiner bolts.

The step-bolts and carabiner bolts may include a base flange between thethreads and the shaft. Use of a base flange significantly reduces thebending stress at the junction between the shaft and the tower wall. Atip flange may also be included to help prevent the user's foot fromslipping off the end of the step-bolt. Optionally, the base flange isblended smoothly into the shaft and the shaft is blended smoothly intothe undercut section in order to reduce stress concentrations.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be better understood from a reading of thefollowing detailed description, taken in conjunction with theaccompanying drawing figures in which like references designate likeelements and, in which:

FIG. 1 is a perspective view of a pair of utility transmission towershaving step-bolts incorporating features of the present invention;

FIG. 2 is a side view of a step-bolt incorporating features of thepresent invention;

FIG. 3 is a perspective view of a carabiner prior to being attached tothe step-bolt of FIG. 2;

FIG. 4 is a perspective view of a carabiner after being attached to thestep-bolt of FIG. 2;

FIG. 5 is a cross sectional view of a carabiner attached to thestep-bolt of FIG. 2;

FIG. 6 is a perspective view of a lineman ascending a tower inaccordance with a method incorporating features of the presentinvention; and

FIG. 7A-7D are cross-sectional views of alternative embodiments of astep-bolt incorporating features of the present invention.

DETAILED DESCRIPTION

The drawing figures are intended to illustrate the general manner ofconstruction and are not necessarily to scale. In the detaileddescription and in the drawing figures, specific illustrative examplesare shown and herein described in detail. It should be understood,however, that the drawing figures and detailed description are notintended to limit the invention to the particular form disclosed, butare merely illustrative and intended to teach one of ordinary skill howto make and/or use the invention claimed herein and for setting forththe best mode for carrying out the invention.

With reference to the drawing figures, FIG. 1 is an illustration of apair of support towers 8 of the type typically used by power companiesfor transmission of electric power. In accordance with the invention,support towers 8 include a plurality of step-bolts 10, which arethreaded into threaded apertures in support towers 8. Step-bolts 10 arespaced apart along the length of the tower to provide a foot purchaseand/or hand grip for a lineman, repairman or other authorized individualto use to ascend and descend the tower.

With additional reference to FIG. 2, each of step-bolts 10 comprises asolid substantially cylindrical elongate body 12, preferably machined,cast, rolled or otherwise formed from a solid round bar of steel,aluminum, titanium or other suitable material. One end 14 of body 12comprises an attachment means, which in the illustrative embodimentcomprises a threaded portion 16, typically with ⅝″ or ¾″ male UNCthreads to match the existing apertures in support tower 8. Step-bolt 10may be secured to tower 8 by threading into a threaded aperture formedin tower 8 or may be secured by a corresponding nut, where it ispossible to access the back side of the aperture with a wrench. Threadsize and the method of attachment should not, however, be considered alimitation of the invention. Other means of attachment, including forexample, insertion of an enlarged head portion of end 14 into a verticalkeyhole slot, forming female threads in end 14, and press/shrinkinterference fit are all considered attachment means within the scope ofthe invention.

Body 12 further includes a shaft portion 18 extending away from threadedportion 16. A base flange 20 approximately 0.175 inches thick and havingan outside diameter of 1½ inches separates shaft portion 18, fromthreaded portion 16. Base flange 16 provides a large bearing surfacebetween step-bolt 10 and support tower 8 to reduce the potential bendingstresses on step-bolt 10 in a fall-arrest situation. Shaft portion 18includes an enlarged section 22 and an undercut region 24, the purposeof which will be explained in further detail hereinafter. Undercutregion 24 is offset toward base flange 20 relative to the full length ofshaft portion 18. The free end 26 of step-bolt 10 terminates at a tipflange 28 approximately ¼ inch thick by 1½ inches in diameter. Tipflange 28 provides a conventional stop to prevent a user's foot fromsliding off the free end 26 of step-bolt 10.

With additional reference to FIGS. 3-7, a carabiner 30 is provided,along with a shock absorbing lanyard 32 and safety harness 34. Thecarabiner may be of any design, but preferably is the type that can bemanipulated by a single hand, such as the “Step Safe Lanyard 2002” soldby Total Access (UK) Ltd, Eccleshall UK. Carabiner 30 includes a gate36, a lock 36 and a basket 40 having a throat 42. In the illustrativeembodiment, with gate 36 closed, throat 42 has a dimension “T” ofslightly more than 3/4 inches as is necessary to attach it to a standard¾ inch step-bolt. Undercut region 24 of step-bolt 10, therefore, ismachined to approximately the same diameter as a standard 3/4 inchstep-bolt for compatibility with carabiner 30. Enlarged section 22 ismachined to approximately 1 inch in diameter. This enables enlargedsection 22 to provides a surface that prevents carabiner 30 from movingoutside of undercut region 24.

Although in the illustrative embodiment, dimension “T” is slightly morethan ¾ inches, in practice, the diameter of undercut region 22 should be0.005 to 0.200 inches, preferably 0.010 to 0.100 inches and mostpreferably about 0.050 less than the actual dimension “T” of thecorresponding carabiner, irrespective of the nominal throat dimension ofthe carabiner. Similarly, although in the illustrative embodiment thediameter of enlarged section 22 is 1 inch, in practice enlarged sectioncan be any diameter that is larger than dimension “T” by a sufficientamount (e.g. 0.050″-0.100″) to prevent carabiner 30 from moving outsideof undercut region 24.

With particular reference to FIG. 6, in accordance with a methodincorporating features of the present invention, a lineman,communications worker or other user 50 ascends tower 8 by attaching acarabiner 30 to one of the step-bolts 10 as hereinbefore described. Theundercut region 24 in combination with the enlarged section 22 retaincarabiner 30 in the undercut region adjacent to the base flange 20 ofstep-bolt 10. This ensures that in the event of a fall, the bendingstresses on step-bolt 10 will be minimized. Once the carabiner 30 isattached to a step-bolt, the user 50 can ascend the tower by steppingonto a different one of the step-bolts 10 and then attaching carabiner30 a to yet another step-bolt. This process is repeated until the user50 has ascended the tower to the desired location and repeated inreverse as the user 50 descends the tower. In an alternative embodiment,carabiner bolts 10 a are provided for attaching carabiner 30 to tower 8.Carabiner bolts are made intentionally too short for user 50 to step on,but are used in conjunction with step-bolts 10, or conventionalstep-bolts, to provide an attachment point for carabiner 30, whilestep-bolts 10, or conventional step-bolts are used for foot and/or handpurchase during ascent and descent.

As can be determined from the foregoing, a major consideration in thedesign of a step-bolt is reducing the bending stress in the step-boltduring a fall arrest. Consequently, the inventor of the presentinvention determined that it would be important to reduce stressconcentrations K_(t) especially in the portions of the step-bolt thatwould be supporting the user in a fall. With reference to FIG. 7A,step-bolt 10 b includes a fillet having a radius R1 which forms a90-degree arc between undercut section 24 b and enlarged region 22 b anda fillet having a radius R2, which forms a 90-degree arc betweenenlarged region 22 b and base flange 20 b. These radii are relativelysmall and, therefore, have a relatively high stress concentration factorK_(t). With reference to FIG. 7B, step-bolt 10 c includes a fillethaving a radius R3 between undercut section 24 b and enlarged region 22c and a fillet having a radius R4, between enlarged region 22 c and baseflange 20 c. R3 and R4 do not form 90 degree arcs and therefore arelarger than R1 and R2. The increase in radius results in a decrease inthe stress concentration factor K_(t). With reference to FIG. 7C,step-bolt 10 d includes a fillet having a blended radius R5 and R6between undercut section 24 d and enlarged region 22 d and a fillethaving a blended radius R7 and R8, between enlarged region 22 d and baseflange 20 d. R6 is larger than R5 and R8 is larger than R7. The compoundcurve resulting from the blended radii further decreases the stressconcentration factor K_(t) relative to a fillet having a constantradius. Finally, with reference to FIG. 7D, step-bolt 10 e includes afillet between undercut section 24 e and enlarged region 22 e. Thefillet has an elliptical profile, so that the radius R9 is continuouslydecreasing moving axially inward from undercut section 24 e towardenlarged section 22 e. Step-bolt 10 e further includes a fillet betweenenlarged region 22 e and base flange 20 e. The fillet has an ellipticalprofile, so that the radius R10 is continuously decreasing movingaxially inward from enlarged section 22 e to base flange 20 e. Thisresults in still further decrease in the stress concentration factorK_(t). A fillet may also optionally be provided between undercut region24 and enlarged region 22 at the free end as shown in FIGS. 7A-7D,although a sharp transition at the free end of undercut region 24 may bemore effective in preventing carabiner 30 from sliding outward alongshaft 18.

Although certain illustrative embodiments and methods have beendisclosed herein, it will be apparent from the foregoing disclosure tothose skilled in the art that variations and modifications of suchembodiments and methods may be made without departing from theinvention. For example, although in the illustrative embodiment, thesupport tower is a power transmission tower, the support tower can beany utility pole, radio tower, or other vertical structure that can beclimbed by a utility worker or other user. Similarly, although theillustrative embodiment discloses a bolt that is machined from a solidbillet of material, the invention is not limited to a unitary bolt, butcould be made from multiple pieces, such as a threaded rod that isthreaded, pressed or otherwise attached to the elongate shaft portion.Additionally, although in the illustrative embodiment undercut region 24is offset toward base flange 20 relative to the full length of shaftportion 18, undercut region 20 could be centered relative to the fulllength of shaft portion 18, or even offset toward the free end 26 ofshaft portion 18. Accordingly, it is intended that the invention shouldbe limited only to the extent required by the appended claims and therules and principles of applicable law.

As used herein, references to direction such as “up” or “down” as wellas recited materials or methods of attachment are intended to beexemplary and are not considered as limiting the invention and, unlessotherwise specifically defined, the terms “generally,” “substantially,”or “approximately” when used with mathematical concepts or measurementsmean within ±10 degrees of angle or within 10 percent of themeasurement, whichever is greater. As used herein, a step of “providing”a structural element recited in a method claim means and includesobtaining, fabricating, purchasing, acquiring or otherwise gainingaccess to the structural element for performing the steps of the method.As used herein, the claim terms are to be given their broadestreasonable meaning unless a clear disavowal of that meaning appears inthe record in substantially the following form (“As used herein the term______ is defined to mean ______”)

1. A method of ascending a support tower comprising: providing a supporttower having first and second step-bolts attached to the support towerso that said first and second step-bolts extend substantiallyhorizontally away from the support tower, said first and secondstep-bolts each comprising a generally elongate body having a first endand a second end, the first end comprising means for attaching to acorresponding location of the support tower, the second end comprisingan elongate shaft portion extending away from the first end andterminating in a free end, the elongate shaft portion comprising anenlarged section, an undercut region and a tip flange each having apredetermined diameter and axial length, the diameter of the undercutregion being less than the diameter of the enlarged section, thediameter of the enlarged section being less than the diameter of the tipflange, the axial length of the undercut region being greater than theaxial length of the tip flange and the axial length of the enlargedsection being greater than the axial length of the undercut region;providing a safety harness and a carabiner attached to the safetyharness, the carabiner having a throat with a predetermined dimension,the predetermined dimension of the throat being smaller than thediameter of the enlarged section of the elongate shaft portion; andattaching the carabiner to the first step-bolt by engaging the throat ofthe carabiner with the undercut region of the step-bolt.
 2. The methodof claim 1, further comprising: stepping onto the second step-bolt toascend the support tower.
 3. The method of claim 1, wherein: thepredetermined dimension of the throat is substantially equal to thediameter of the undercut region.
 4. The method of claim 1, wherein: thepredetermined dimension of the throat is 0.005 to 0.100 larger than thediameter of the undercut region.
 5. The method of claim 1, wherein: thestep-bolt further comprises a base flange disposed between the first endand the elongate shaft portion, the base flange having a diameter thatis larger than the diameter of the elongate shaft portion.
 6. (canceled)7. The method of claim 1, wherein: the undercut region is centered abouta mid-point of the step-bolt.
 8. The method of claim 1, wherein: theundercut region is offset relative to a mid-point of the step-bolt. 9.The method of claim 1, wherein: the diameter of the undercut region isblended into the diameter of the elongate shaft portion with a 90-degreefillet.
 10. The method of claim 1, wherein: the diameter of the undercutregion is blended into the diameter of the elongate shaft portion withan ogival fillet.
 11. The method of claim 1, wherein: the diameter ofthe undercut region is blended into the diameter of the elongate shaftportion with a fillet comprising two arcs having different radii. 12.The method of claim 1, wherein: the diameter of the undercut region isblended into the diameter of the elongate shaft portion with a filletcomprising two elliptical splines that are tangent to the surface of thestep-bolt at their smallest circumference.
 13. The method of claim 1,wherein: the diameter of the elongate shaft portion is blended into thediameter of the base flange with a 90-degree fillet.
 14. The method ofclaim 1, wherein: the diameter of the elongate shaft portion is blendedinto the diameter of the base flange with an ogival fillet.
 15. Themethod of claim 1, wherein: the diameter of the elongate shaft portionis blended into the diameter of the base flange with a fillet comprisingtwo arcs having different radii.
 16. The method of claim 1, wherein: thediameter of the elongate shaft portion is blended into the diameter ofthe base flange with a fillet comprising two elliptical splines that aretangent to the surface of the step-bolt at their smallest circumference.17. In combination with a support tower, a step-bolt comprising: agenerally elongate body having a first end and a second end, the firstend comprising means for attaching to a corresponding location of thesupport tower, the second end comprising an elongate shaft portionextending away from the first end and terminating in a free end, theelongate shaft portion comprising an enlarged section, an undercutregion and a tip flange each having a predetermined diameter and axiallength, the diameter of the undercut region being less than the diameterof the enlarged section, the diameter of the enlarged section being lessthan the diameter of the tip flange, the axial length of the undercutregion being greater than the axial length of the tip flange and theaxial length of the enlarged section being greater than the axial lengthof the undercut region.
 18. The step-bolt of claim 17, furthercomprising: a base flange disposed between the first end and theelongate shaft portion, the base flange having a diameter that is largerthan the diameter of the elongate shaft portion.